Wood preservative chemicals such as creosote, creosote-coal tar solutions, creosote-petroleum oil solutions, pentachlorophenols, pentachlorophenol-petroleum oil solutions and the like, have been widely used to treat a variety of wood products. These products include, for example, railroad ties, switch ties, poles, posts, structural timbers, and the like. However, in the course of treating such wood products with these particular wood preservative chemicals, substantial quantities of waste waters are produced which can contain anywhere from trace amounts to about 50 percent or more of these wood preservative chemicals.
One method for handling these contaminated waste waters has been to contain them in surface impoundments or ponds. With time, these waste waters can, and do, undergo separation into discrete layers of water and a wood preservative chemical. Once formed, these discrete layers then can be, and generally are, separately withdrawn from the impoundment or pond. The water layer recovered from the impoundment or pond is treated for subsequent disposal while the wood preservative chemical layer is, most usually, dehydrated and then recycled for reuse in the treatment of further wood products.
The above method for the recovery of the wood preservative chemical from such surface impoundments or ponds is both limited and inefficient at best. This is due in part to the fact that a substantial portion of the wood preservative chemical in the waste waters contained in the surface impoundment or pond forms a stable water emulsion. This water emulsion settles onto the bottom of the impoundment or pond as a thick, congealed semisolid or sludge. Usually, no effort is made to recover the wood preservative chemical from this sludge even though it can comprise from about 40 to about 90 percent by weight of the total weight of the sludge. In those instances where the sludge is removed from the surface impoundment or pond such as, for example for purposes of closing the impoundment or pond, the sludge merely is solidified for subsequent storage in environmentally secured waste sites.